Semiconductor light emitting devices such as light emitting diodes (LEDs) are among the most efficient light sources currently available. Material systems currently of interest in the manufacture of high brightness LEDs capable of operation across the visible spectrum include group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials; and binary, ternary, and quaternary alloys of gallium, aluminum, indium, arsenic, and phosphorus. Often III-nitride devices are epitaxially grown on sapphire, silicon carbide, or III-nitride substrates and III-phosphide devices are epitaxially grown on gallium arsenide by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. Often, an n-type region is deposited on the substrate, then a light emitting or active region is deposited on the n-type region, then a p-type region is deposited on the active region. The order of the layers may be reversed such that the p-type region is adjacent to the substrate.
One promising use of semiconductor light emitting devices is for backlights for general illumination and display devices such as liquid crystal displays (LCDs). Color or monochrome transmissive LCDs are commonly used in cellular phones, personal digital assistants, portable music players, laptop computers, desktop monitors, and television applications.
One example of a backlight where light is provided by LEDs is illustrated in FIG. 5 is described in U.S. Pat. No. 7,052,152. An array of LEDs 43 is placed on the rear panel of the backlight 45. The back plane 48 and sidewalls 46 of the backlight 45 are covered with highly reflective materials. A color converting phosphor layer 47 is disposed on a cover plate 40 of backlight 45. LCD panel 44 is placed in front of backlight 45. LCD panel 44 may be a conventional LCD, having a first polarizing filter, a thin film transistor array for developing an electric field across selected areas of the liquid crystal layer, a liquid crystal layer, an RGB color filter array, and a second polarizing filter. The color filter array has red, green and blue subpixels. Between the LCD panel 44 and the backlight 45, additional films are often used, such as a brightness enhancement film (BEF) or polarization recovery film (DBEF).